DE112004001360T5 - Acoustic transducer - Google Patents

Abstract

Acoustic transducer for measuring a property of a fluid comprising:
an acoustic pulse generator;
an impedance matching layer between the pulse generator and the fluid, wherein the matching layer is formed of a low thermal conductivity material; and a thermal management system attached to the matching layer for dissipating heat therefrom, wherein the management system is formed of a material having a high thermal conductivity opposite to the matching layer and disposed along the matching layer such that a significant amount of heat from the thermal management system arrives the environment is released without excessive temperature rise at the pulse generator.

Description

THE iNVENTION field

The The present invention relates to acoustic transducers, including such which are used in flow meters.

The transmission of pulses of acoustic energy through a fluid is useful for measuring the condition and properties of a fluid, especially velocity and temperature. In acoustic transducers, piezoceramic elements are generally used to generate ultrasound acoustic pulses or continuous wave fields. However, these ceramics lose polarization when exposed to temperatures exceeding half the Curie point. For commercially available ceramics this limits the operating temperature of the ceramic to below 200 ° C. In order to operate in fluids above this temperature, one method is to provide a buffer or delay line between the piezoceramic element and the fluid (eg, exhaust gas or exhaust gas), as in FIG 1 is shown. 1 shows an acoustic transducer 10 , The transducer comprises a piezoceramic element 12 and a buffer 14 that goes through a wall 16 extends into the fluid, which is shown as exhaust gas or exhaust gas. In the buffer 14 Thermal energy is transferred to an internal convective boundary layer 18 and at an external convective boundary layer 20 delivered when heat in the buffer 14 is guided upward to the piezoceramic element. Buffers work according to Fourier's law of heat conduction: q''κ = -κVT where q '' is the heat flux, κ is the thermal conductivity and T is the temperature. Detailed solutions to this equation require numerical methods, but with some simplifying assumptions, a buffering system can be reduced to a more concentrated parameter model, known as the in 2 shown equivalent circuit can be displayed. 2 illustrates the exhaust, the buffer tip, the crystal and ambient temperatures, and the thermal resistances of the external convective boundary layer, the buffer, and the internal convective boundary layer in a concentrated parameter model.

For the in 2 The concentrated parameter model shown is the temperature of the crystal:

One The disadvantage associated with existing buffer systems is that the existence short buffer has problems when working with hot fluids while then if the buffer is longer is made, it is necessary that the buffer is the wavefront in the desired Direction leads. However, fixed buffers fail to effectively carry the acoustic pulse, resulting in a dispersive buffer, which is the ultrasound pulse distorted and usefulness limited the flow meter.

additional Background information can in U.S. Patent Nos. 5,756,360; 4,336,719; 5,217,018; 5,159,838; 6,343,511, 5,241,287, 4,743,870.5, 438,999, 4,297,607 and 6,307,302 being found.

Out the above reasons There is a need for an improved acoustic transducer.

Summary the invention

It It is an object of the present invention to provide an acoustic transducer to create one against heat includes shielded acoustic matching coupler with integral cooling.

In the practice of the present invention, an acoustic transducer is provided. The transducer includes an acoustic pulse generator, an impedance matching layer, and a thermal management system. The acoustic transducer is used to measure a fluid property. The impedance matching layer is located between the pulse generator and the fluid. The adaptation layer is made of a material with low thermal conductivity. The thermal management system is attached to the matching layer to transfer heat from the matching layer. The thermal management system is formed of a material having a high thermal conductivity with respect to the matching layer. The thermal management system is arranged along the matching layer such that a significant amount of heat is released to the environment from the thermal management system without excessive temperature rise at the pulse generator.

Of the Acoustic pulse generator is preferably a piezoceramic element for generating an ultrasound pulse. An impedance matching layer type a buffer is similar to a traditional buffer but has one reduced length to the point where migratory waves are no longer present and the problems associated with waveguides do not matter. Different expressed the impedance matching layer is of a thickness small enough is that yourself form standing waves. Preferably, the pulse generator is such configured that he works at a certain frequency, and the adjustment layer has a thickness that is an odd multiple of the quarter wavelength (λ / 4, 3λ / 4, 5λ / 4, ...) of the sound in the adaptation layer for the particular frequency of the Pulse generator approximately is equal to. Preferably, the thermal conductivity the matching layer is less than 15 W / (m.K). Even more preferred a thermal conductivity the matching layer is less than 1W / (m.K). The adjustment layer may be made of silica, preferably of foamed silica. Naturally can alternatively ceramics or other materials as an adaptation layer be used. When making the matching layer of a lightweight material with low thermal conductivity, that is more resistant to corrosion than the body of the transducer, a metallic sealing layer is not needed and the matching layer can be in direct contact with the fluid being measured is, or a light or thin anti-reflective surface coating exhibit.

The thermal management system can regarding its material and its configuration vary, provided that of the Thermal management system transfer a significant amount of heat into the environment is, without excessive temperature increase on Pulse generator. Preferably the thermal conductivity of the thermal management system at least 15 W / (m.K). Even more preferable is the thermal conductivity of the thermal management system at least 100 W / (m.K). The preferred one thermal management system includes a plurality of on the holder attached fins to heat low on the body to distribute the adapter.

During the In operation, at least a portion of the sides of the adaptation layer extend and the tip of the matching layer into the fluid, straight is measured. In a preferred embodiment, the thermal management system is arranged so that it is the part of the sides of the matching layer isolated from the heat of the fluid while the top of the matching layer is left in contact with the fluid. This can be done by isolation reaches the part of the sides of the matching layer by means of an air gap which is formed by the thermal management system. Finally includes in the preferred application, the thermal management system Sleeve over the Adjustment layer to heat from to transfer the adaptation layer.

Further will be in the execution The invention relates to an acoustic transducer in combination with a device created, comprising a conduit through which a fluid flows. The Combination uses various of the features described above. The device may include a device for sampling or testing be exhaust gas or exhaust gas.

Further will be in the execution invention provides a sampling system. The system includes a Fluid inlet for intake a fluid, a dilution inlet for receiving a diluent gas, a mixing section for the mixture of at least part of the fluid with the diluent gas, and a collection section for the Collect a sample of the mixture. The system further includes a flow meter for measuring a connected to the sample system Flow. The flowmeter comprises an acoustic transducer for measuring the flow. Of the Instrument transformer uses various features described above. at an arrangement The flow meter uses a pair of acoustic transducers for measurement the flow opposite each other are arranged in a conduit through which the fluid flows.

Further, in the practice of the invention, a sampling system is provided. The system includes a sampling line for taking samples of a fluid from a main conduit, and a flowmeter for measuring a flow of the fluid through the main conduit. The flowmeter includes an acoustic transducer for measuring the flow. The system further includes a ver a dilution inlet for receiving a diluent gas, a mixing section for mixing the fluid flow from the sampling line with the diluent gas in a generally fixed ratio, and a sample control collection section of the mixture. The mixture is tested at intervals or at a rate generally proportional to the flow of fluid through the main conduit. The transducer uses various of the features described above. In one arrangement, the flowmeter comprises a pair of acoustic transducers disposed opposite one another in the main conduit.

The with the embodiments The advantages associated with the present invention are numerous. For example, preferred embodiments of the present invention provide Invention an acoustic transducer, the shielded against heat Includes acoustic matching coupler with integral cooling, wherein the matching layer has attached to her thermal management system, such that the thermal Management system considerable heat transferred to the environment is, without excessive temperature increase on Pulse generator.

The The above object and other objects, features and advantages of the present Invention will be apparent from the following detailed description of the preferred embodiment in conjunction with the attached Drawings apparently.

Short description the drawings

1 shows a use of a buffer according to the prior art;

2 shows an electrical equivalent circuit of the thermal buffer assembly after 1 ;

3 shows an acoustic transducer according to the present invention;

4 shows an electrical equivalent circuit of in 3 illustrated acoustic transducer assembly;

5 shows a pocket mini thinner sampling system according to the present invention; and

6 shows a flow meter in the system 5 ,

Single Description the preferred embodiment

3 shows an acoustic transducer 30 for measuring a property of a fluid. The transducer 30 comprises a piezoelectric element 32 and a buffer 34 of the impedance matching layer type extending through the wall 36 a conduit through which the fluid flows. The conduit is part of a device in which the acoustic transducer 30 is used. The impedance matching layer 34 is made of a material of low thermal conductivity and low weight and is preferably made of foamed silica. The impedance matching layer is of a thickness small enough to form standing waves. The thickness should be an odd multiple of the quarter wavelength of the sound in the matching layer for the particular frequency of the pulse generator. The transducer 30 Also includes a thermal management system made of a metal sleeve 37 above the adjustment layer 34 and the piezoelectric element 32 is composed.

The sleeve 37 extends through the wall 36 and a metal sign 38 with a small air gap in between and the matching layer 34 forms a high contact resistance compared to the convective thermal boundary layer 40 , The metal shield 38 also protects the buffer during installation and operation. The buffer tip is using a baked glass insert 43 on the metal sign 38 sealed. The adjustment layer 34 can with an anti-reflective coating 45 be coated from an ultra-light material such as an airgel to increase the signal quality. On the sleeve 37 that the piezoelectric element 32 Finns can 42 be appropriate to from below on the body of the adjustment layer 34 Dissipate heat. An epoxy seal glues the sleeve 37 with minimal contact resistance to the matching layer buffer 34 to release heat through the fins 42 of the thermal management system. An isolation ring 44 prevents direct heat transfer from the shield 38 to the sleeve 37 and keeps the crystal at the same temperature as the sleeve 37 , 4 with an equivalent electrical circuit illustrates the exhaust gas, the buffer tip, the crystal and the ambient temperatures, as well as the thermal resistances of the convective boundary layer 40 , the buffer 34 and the Finns 42 , The buffer resistance is shown with part of the resistance in front of the fins 42 and with part of the resistance behind the Finns 42 to the distribution of heat from the lower part of the body of the adjustment layer 34 to design.

It is appreciated that the conformal layer of low thermal conductivity material and the thermal management system are formed of high thermal conductivity material, the latter being disposed along the conformance layer such that significant heat is emitted from the fins 42 is transferred to the environment, without an excessive increase in temperature on the piezoceramic element. That is, the design can be varied many times while still achieving a suitable thermal management solution, provided that the buffer remains small enough to act as an impedance matching layer and the thermal management system is low enough in the matching system. The materials of the matching layer and their properties may vary depending on the configuration and other aspects of the thermal management system, e.g. B. depending on the surface area of the fins.

5 clarified at 60 a pocket mini thinner sampling system. The sampling system comprises a main conduit with an inlet 62 for the absorption of the exhaust gas. The flow meter 64 measures the fluid flow through the main pipe and accumulates the total exhaust gas volume. The flowmeter provides a direct exhaust flow measurement signal and has at least one acoustic transducer in accordance with the present invention. Depending on the realization, a blower 66 assist in fluid flow through the conduit.

A sampling line 68 takes exhaust samples from the main line. A dilution inlet 70 receives a diluent gas. A stationary flow monitoring 72 and a steady flow monitoring 74 (Mass flow monitors or critical flow venturis) each monitor the flow of diluent gas and sampled exhaust gas to create a generally fixed ratio in the mixing zone. A pump 76 pumps the mixture of diluent gas and exhaust sample for possible collection in bags 82 , A proportional flow device 78 provides an inflow to the sample collecting bags 82 which is proportional to the flow through the main. Accordingly, a bypass is provided to allow some of the mixture to flow past the collectors.

6 illustrates the flow meter 64 in more detail, showing a pair of acoustic transducers 30 which are arranged opposite each other across the conduit.

During embodiments The invention has been shown and described, it is not intended that this embodiments all possible Illustrate and describe forms of the invention. Much more the words used in these documents are those the description and not those of limitation and it is understood that many changes can be made without departing from the spirit and scope of the invention.

SUMMARY

An acoustic transducer ( 30 ) comprises an acoustic pulse generator ( 32 ), an impedance matching layer ( 34 ) and a thermal management system ( 37 . 42 ). The thermal management system is attached to the matching layer to dissipate heat therefrom and is formed of a material having a high thermal conductivity with respect to the matching layer. The thermal management system is disposed along the matching layer so that a significant amount of heat is released to the environment by the thermal management system without excessive temperature rise at the pulse generator.

Claims (27)

An acoustic transducer for measuring a property of a fluid, comprising: an acoustic pulse generator; an impedance matching layer between the pulse generator and the fluid, wherein the matching layer is formed of a low thermal conductivity material; and a thermal manage The system is mounted on the matching layer to dissipate heat therefrom, wherein the management system is formed of a material having a high thermal conductivity over the matching layer and disposed along the matching layer such that a significant amount of heat is released from the thermal management system to the environment without excessive temperature rise at the pulse generator. Acoustic transducer according to claim 1, wherein the thermal conductivity the matching layer is less than 15 W / (m.K). Acoustic transducer according to claim 1, wherein the thermal conductivity the matching layer is less than 1 W / (m.K). Acoustic transducer according to claim 1, wherein the adaptation layer of foamed Silica is made. Acoustic transducer according to claim 1, wherein the matching layer is made of silica. Acoustic transducer according to claim 1, wherein the thermal conductivity of the thermal management system is at least 15 W / (m.K). Acoustic transducer according to claim 1, wherein the thermal conductivity of the thermal management system is at least 100 W / (m.K). Pulse generator, which is configured so that it An acoustic transducer according to claim 1, wherein the particular Frequency works, and the matching layer has a thickness, which is an odd multiple of the quarter wavelength of the Sound in the adaptation layer for the particular frequency of the Pulse generator approximately is equal to. Acoustic transducer according to claim 1, wherein the thermal management system comprises a plurality of fins. Acoustic transducer according to claim 1, wherein the acoustic generator is a piezoelectric element for generating an ultrasonic pulse. Acoustic transducer according to claim 1, wherein the matching layer has a surface coating, which is in contact with the fluid being measured. Acoustic transducer according to claim 1, wherein while at least part of the pages and the top of the page Extend adjustment layer into the fluid being measured and wherein the thermal management system is arranged Is that it is the part of the sides of the adaptation layer of the heat of the Fluids isolated while it leaves the tip of the matching layer in contact with the fluid. Acoustic transducer according to claim 12, wherein the isolated parts of the sides of the matching layer by means of a Air gap isolated from the thermal management system is formed. Acoustic transducer for measuring a property a fluid comprising: one acoustic pulse generator; an impedance matching layer between the pulse generator and the fluid, wherein the matching layer of a material with a thermal conductivity is formed, the smaller is 1 W / (m.K); and a thermal management system that has a Sleeve over the Adaptation layer has to heat dissipate from the adaptation layer, wherein the thermal management system of a material with respect to the Adaptation layer formed high thermal conductivity and such along the Matching layer is arranged that of the thermal management system a considerable amount of heat is released to the environment, without an excessive increase in temperature on the pulse generator. Acoustic transducer according to claim 14, wherein the thermal conductivity of the thermal management system is at least 15 W / (m.K). Acoustic transducer according to claim 14, wherein the thermal conductivity of the thermal management system is at least 100 W / (m.K). Acoustic transducer according to claim 14, wherein the pulse generator is configured to operate at a particular frequency works and the matching layer has a thickness equal to one odd multiples of the quarter wavelength of the sound in the matching layer for the certain frequency of the pulse generator is approximately equal. Acoustic transducer according to claim 14, wherein the thermal management system comprises a plurality of fins, extending from the sleeve outward extend. Acoustic transducer according to claim 14, wherein the acoustic generator is a piezoelectric element for generating an ultrasonic pulse. Acoustic transducer according to claim 14, wherein the matching layer has a surface coating, which is in contact with the fluid being measured. Acoustic transducer according to claim 14, wherein while at least part of the pages and the top of the page Extend adjustment layer into the fluid being measured and wherein the thermal management system is arranged Is that it is the part of the sides of the adaptation layer of the heat of the Fluids isolated while it leaves the tip of the matching layer in contact with the fluid. Acoustic transducer according to claim 21, wherein the isolated parts of the sides of the matching layer by means of a Air gap isolated from the thermal management system is formed. In combination with a device that has a lead has, in which a fluid flows, the improvement which comprises: one acoustic transducer for measuring a property one Fluids, which owns an acoustic pulse generator, a Impedance matching layer and a thermal management system, wherein the impedance matching layer is between the pulse generator and the fluid is the matching layer of a material with low thermal conductivity is formed, and the thermal management system at the adaptation layer attached to dissipate heat from the same, and the management system made of a material with a high compared to the matching layer thermal conductivity formed and such longitudinal the adaptation layer is arranged that of the thermal management system a considerable amount of heat is released to the environment, without an excessive increase in temperature on the pulse generator. Sampling system with a fluid inlet for the Receiving a fluid; a dilution inlet for intake a diluent gas; one Mixing section for mixing at least a portion of the fluid with the diluent gas; one Collection section for collecting a sample of the mixture; and a flow meter for measuring the flow with respect to the sampling system, wherein the flowmeter comprises a acoustic transducer for measuring the flow, which has one acoustic pulse generator, an impedance matching layer and a thermal management system, wherein the impedance matching layer is between the pulse generator and the fluid, the matching layer made of a material with low thermal conductivity is formed, and the thermal management system at the adaptation layer attached to dissipate heat from the same, and the management system made of a material with a high compared to the matching layer thermal conductivity formed and such longitudinal the adaptation layer is arranged that of the thermal management system a considerable amount of heat is released to the environment, without an excessive increase in temperature on the pulse generator. A sampling system according to claim 24, wherein the flow meter a pair of acoustic transducers, which measure the flow opposite each other are arranged in a conduit through which the fluid flows. Sampling system with: a sampling line for taking samples of a fluid from a main conduit; a flowmeter for measuring a flow of fluid through the main conduit, the flowmeter including a flow rate acoustic transducer which in turn comprises an acoustic pulse generator, an impedance matching layer and a thermal management system, the impedance matching layer being between the pulse generator and the fluid, the matching layer is formed of a material having a low thermal conductivity, and the thermal management system is attached to the matching layer to dissipate heat therefrom, and wherein the management system is formed of a material having a high thermal conductivity superior to the matching layer and thus arranged along the matching layer is that a significant amount of heat is released from the thermal management system to the environment, without an excessive increase in temperature at the pulse generator. A sampling system according to claim 26, wherein the flow meter has a pair of acoustic transducers, that for measuring the flow opposite each other in a line are arranged, through which the fluid flows.